The present invention relates generally to bioreactor processing within a tank, involving filtration through membranes after biological treatment to remove solid contaminants.
Membrane bioreactor systems have been utilized on-board commercial vessels to treat influent waste such as wastewater derived from various sources so as to: (a) eliminate perturbations in flow and temperature, (b) reduce biochemical oxygen demand, (c) reduce total suspended contaminating solids and (d) reduce fecal coliform concentration. Such systems involve collection of raw, non-oily wastewater fed into a tank for processing by membrane filtration and biological treatment to induce growth of the aerobic bacteria therein, promoted by aeration and carbon dissolved in the wastewater embodied in the solids carried therein. The wastewater so processed is withdrawn with reductions in biological oxygen demand, total suspended solids, and fecal coliform concentrations.
The maximum organic and hydraulic load capability of such bioreactor systems is limited by size of bioreactor tanks, concentration of contaminating solids within the wastewater being processed and the number of membranes through which permeate filtration is performed. While performing filtration on wastewater with or near the maximum allowable solids concentration therein, in a bioreactor system having a reduced size for shipboard installation, fouling of the membranes associated therewith increases so as to limit their operational life and require frequent cleaning and/or replacement. It is therefore an important object of the present invention to reduce temporary and permanent fouling of the membranes associated with such bioreactor systems so as to provide a more viable processing method, especially on-board sea vessels having limited installation space.
In accordance with the present invention, a single tank is utilized in a bioreactor system, internally partitioned into a volumetrically large chamber within which biological treatment of a wastewater contaminated by solids suspended therein, is continuously performed, and a volumetrically small chamber within which membrane filtration is performed after the wastewater collected within the small chamber undergoes separation between portions thereof by a dewatering device, located outside of the tank. Separation of such portions of the wastewater respectively increases and lowers contamination so that the portion with lowered contamination may undergo filtration into a cleansed effluent to be withdrawn, reflective of maximized removal of suspended solids during processing of wastewater contaminated under different conditions. Selectively controlled valve means is associated with the system in order to interrupt membrane filtration performed within the small chamber of the lank, while the separated portion with increased contamination is continuously recycled into the large chamber for biological retreatment. Also, some of the separated portion of the wastewater with the lowered contamination is disposed of by direct discharge from the dewatering device in by-pass relation to the tank, when the contamination condition does not require membrane filtration.